Bottom Line:
Using a high-throughput screening approach on cardiac sarcoplasmic reticulum membranes isolated from pig and rat and nicotinamide hypoxanthine dinuleotide as a surrogate substrate, we have identified potent and selective inhibitors of an intracellular, membrane-bound cardiac ADPRC that are different from the two known mammalian ADPRCs, CD38 and CD157/Bst1.We show that two structurally distinct cardiac ADPRC inhibitors, SAN2589 and SAN4825, prevent the formation of spontaneous action potentials in guinea pig papillary muscle in vitro and that compound SAN4825 is active in vivo in delaying ventricular fibrillation and cardiac arrest in a guinea pig model of Ca(2+) overload-induced arrhythmia.Inhibition of cardiac ADPRC prevents Ca(2+) overload-induced spontaneous depolarizations and ventricular fibrillation and may thus provide a novel therapeutic principle for the treatment of cardiac arrhythmias.

ABSTRACTADP-ribosyl cyclases (ADPRCs) catalyse the conversion of nicotinamide adenine dinucleotide to cyclic adenosine diphosphoribose (cADPR) which is a second messenger involved in Ca(2+) mobilisation from intracellular stores. Via its interaction with the ryanodine receptor Ca(2+) channel in the heart, cADPR may exert arrhythmogenic activity. To test this hypothesis, we have studied the effect of novel cardiac ADPRC inhibitors in vitro and in vivo in models of ventricular arrhythmias. Using a high-throughput screening approach on cardiac sarcoplasmic reticulum membranes isolated from pig and rat and nicotinamide hypoxanthine dinuleotide as a surrogate substrate, we have identified potent and selective inhibitors of an intracellular, membrane-bound cardiac ADPRC that are different from the two known mammalian ADPRCs, CD38 and CD157/Bst1. We show that two structurally distinct cardiac ADPRC inhibitors, SAN2589 and SAN4825, prevent the formation of spontaneous action potentials in guinea pig papillary muscle in vitro and that compound SAN4825 is active in vivo in delaying ventricular fibrillation and cardiac arrest in a guinea pig model of Ca(2+) overload-induced arrhythmia. Inhibition of cardiac ADPRC prevents Ca(2+) overload-induced spontaneous depolarizations and ventricular fibrillation and may thus provide a novel therapeutic principle for the treatment of cardiac arrhythmias.

Mentions:
A diverse collection of 17,567 small-molecule compounds was screened at 10-μM concentration for inhibitors of pig heart ADPR cyclase (Fig. 2). All compounds without autofluorescence observed at t = 0 that gave >38.2 % inhibition (mean percent inhibition plus three standard deviations) were considered as screening hits and re-tested over the concentration range between 0.3 and 40 μM; 71 compounds with a concentration response and IC50 values below 40 μM could be identified. After clustering and testing of compounds with related structures, two structural series could be identified with activities of their most potent compounds being in the single-digit nanomolar range. This is several orders of magnitude more potent than the only previously described inhibitor of a non-CD38/CD157 mammalian ADPR cyclase, dihydroxyazobenzene, which was found to have an IC50 value of >100 μM (Fig. 3), which is in good agreement with published data (Nam et al. 2006). Further details and structure–activity relationships for the two series will be described elsewhere.Fig. 2

Mentions:
A diverse collection of 17,567 small-molecule compounds was screened at 10-μM concentration for inhibitors of pig heart ADPR cyclase (Fig. 2). All compounds without autofluorescence observed at t = 0 that gave >38.2 % inhibition (mean percent inhibition plus three standard deviations) were considered as screening hits and re-tested over the concentration range between 0.3 and 40 μM; 71 compounds with a concentration response and IC50 values below 40 μM could be identified. After clustering and testing of compounds with related structures, two structural series could be identified with activities of their most potent compounds being in the single-digit nanomolar range. This is several orders of magnitude more potent than the only previously described inhibitor of a non-CD38/CD157 mammalian ADPR cyclase, dihydroxyazobenzene, which was found to have an IC50 value of >100 μM (Fig. 3), which is in good agreement with published data (Nam et al. 2006). Further details and structure–activity relationships for the two series will be described elsewhere.Fig. 2

Bottom Line:
Using a high-throughput screening approach on cardiac sarcoplasmic reticulum membranes isolated from pig and rat and nicotinamide hypoxanthine dinuleotide as a surrogate substrate, we have identified potent and selective inhibitors of an intracellular, membrane-bound cardiac ADPRC that are different from the two known mammalian ADPRCs, CD38 and CD157/Bst1.We show that two structurally distinct cardiac ADPRC inhibitors, SAN2589 and SAN4825, prevent the formation of spontaneous action potentials in guinea pig papillary muscle in vitro and that compound SAN4825 is active in vivo in delaying ventricular fibrillation and cardiac arrest in a guinea pig model of Ca(2+) overload-induced arrhythmia.Inhibition of cardiac ADPRC prevents Ca(2+) overload-induced spontaneous depolarizations and ventricular fibrillation and may thus provide a novel therapeutic principle for the treatment of cardiac arrhythmias.

ABSTRACTADP-ribosyl cyclases (ADPRCs) catalyse the conversion of nicotinamide adenine dinucleotide to cyclic adenosine diphosphoribose (cADPR) which is a second messenger involved in Ca(2+) mobilisation from intracellular stores. Via its interaction with the ryanodine receptor Ca(2+) channel in the heart, cADPR may exert arrhythmogenic activity. To test this hypothesis, we have studied the effect of novel cardiac ADPRC inhibitors in vitro and in vivo in models of ventricular arrhythmias. Using a high-throughput screening approach on cardiac sarcoplasmic reticulum membranes isolated from pig and rat and nicotinamide hypoxanthine dinuleotide as a surrogate substrate, we have identified potent and selective inhibitors of an intracellular, membrane-bound cardiac ADPRC that are different from the two known mammalian ADPRCs, CD38 and CD157/Bst1. We show that two structurally distinct cardiac ADPRC inhibitors, SAN2589 and SAN4825, prevent the formation of spontaneous action potentials in guinea pig papillary muscle in vitro and that compound SAN4825 is active in vivo in delaying ventricular fibrillation and cardiac arrest in a guinea pig model of Ca(2+) overload-induced arrhythmia. Inhibition of cardiac ADPRC prevents Ca(2+) overload-induced spontaneous depolarizations and ventricular fibrillation and may thus provide a novel therapeutic principle for the treatment of cardiac arrhythmias.